Enzyme mediated generation of organohalogens may serve as an alternate source of halogenated polluants. Haloperoxidases will be incubated with chloride or bromide ions and various organic substrates. The substrates will include beta-keto acids and phenols which are known natural products and/or which are present in the biosphere. These reactions will attempt to determine if haloforms, halophenols and phenolic coupling products (biphenyls, dibenzodioxins, dibenzofurans, etc.) are formed by physiological functions. As an approach to simulating environmental conditions the effect of pH on the type and quantity of reaction products will be investigated. Comparison of isolated products will be made with known structures of halogenated pollutants. The experimental reslts may aid in determining how certain halogenated compounds are produced and metabolized in the environment by microbiologcal processes. Haloperoxidase catalyzed reactions may be useful in predicting baseline concentrations of halogenated substances in the environment.